I gather it's so he can interrupt Alito to snottily condemn him even further. Plus he doesn't want to let Alito answer his questions because it ruins his own rhythm (and Alito would probably smack him down hard).
Schumer is talking to Alito like he'd talk to his 14-year-old son.
I just got home from work and have to see this. I could do violence to Schumer. What a pussy.